hello];
my $processed = $hr->process( $html );
# $processed now equals: hello
DESCRIPTION
This module uses HTML::Parser to strip HTML from text in a restrictive
manner. By default all HTML is restricted. You may alter the default
behaviour by supplying your own tag rules.
CONSTRUCTOR AND STARTUP
new()
Creates and returns a new HTML::Restrict object.
my $hr = HTML::Restrict->new()
HTML::Restrict doesn't require any params to be passed to new. If your
goal is to remove all HTML from text, then no further setup is required.
Just pass your text to the process() method and you're done:
my $plain_text = $hr->process( $html );
If you need to set up specific rules, have a look at the params which
HTML::Restrict recognizes:
* "rules => \%rules"
Sets the rules which will be used to process your data. By default
all HTML tags are off limits. Use this argument to define the HTML
elements and corresponding attributes you'd like to use.
Essentially, consider the default behaviour to be:
rules => {}
Rules should be passed as a HASHREF of allowed tags. Each hash value
should represent the allowed attributes for the listed tag. For
example, if you want to allow a fair amount of HTML, you can try
something like this:
my %rules = (
a => [qw( href target )],
b => [],
caption => [],
center => [],
em => [],
i => [],
img => [qw( alt border height width src style )],
li => [],
ol => [],
p => [qw(style)],
span => [qw(style)],
strong => [],
sub => [],
sup => [],
table => [qw( style border cellspacing cellpadding align )],
tbody => [],
td => [],
tr => [],
u => [],
ul => [],
);
my $hr = HTML::Restrict->new( rules => \%rules )
Or, to allow only bolded text:
my $hr = HTML::Restrict->new( rules => { b => [] } );
Allow bolded text, images and some (but not all) image attributes:
my %rules = (
b => [ ],
img => [qw( src alt width height border / )
);
my $hr = HTML::Restrict->new( rules => \%rules );
Since HTML::Parser treats a closing slash as an attribute, you'll
need to add "/" to your list of allowed attributes if you'd like
your tags to retain closing slashes. For example:
my $hr = HTML::Restrict->new( rules =>{ hr => [] } );
$hr->process( ""); # returns:
my $hr = HTML::Restrict->new( rules =>{ hr => [qw( / )] } );
$hr->process( ""); # returns:
HTML::Restrict strips away any tags and attributes which are not
explicitly allowed. It also rebuilds your explicitly allowed tags
and places their attributes in the order in which they appear in
your rules.
So, if you define the following rules:
my %rules = (
...
img => [qw( src alt title width height id / )]
...
);
then your image tags will all be built like this:
This gives you greater consistency in your tag layout. If you don't
care about element order you don't need to pay any attention to
this, but you should be aware that your elements are being
reconstructed rather than just stripped down.
As of 2.1.0, you can also specify a regex to be tested against the
attribute value. This feature should be considered experimental for
the time being:
my $hr = HTML::Restrict->new(
rules => {
iframe => [
qw( width height allowfullscreen ),
{ src => qr{^http://www\.youtube\.com},
frameborder => qr{^(0|1)$},
}
],
img => [ qw( alt ), { src => qr{^/my/images/} }, ],
},
);
my $html = '';
my $processed = $hr->process( $html );
# $processed now equals:
* "trim => [0|1]"
By default all leading and trailing spaces will be removed when text
is processed. Set this value to 0 in order to disable this
behaviour.
* "uri_schemes => [undef, 'http', 'https', 'irc', ... ]"
As of version 1.0.3, URI scheme checking is performed on all href
and src tag attributes. The following schemes are allowed out of the
box. No action is required on your part:
[ undef, 'http', 'https' ]
(undef represents relative URIs). These restrictions have been put
in place to prevent XSS in the form of:
click for cookie!
See URI for more detailed info on scheme parsing. If, for example,
you wanted to filter out every scheme barring SSL, you would do it
like this:
uri_schemes => ['https']
This feature is new in 1.0.3. Previous to this, there was no schema
checking at all. Moving forward, you'll need to whitelist explicitly
all URI schemas which are not supported by default. This is in
keeping with the whitelisting behaviour of this module and is also
the safest possible approach. Keep in mind that changes to
uri_schemes are not additive, so you'll need to include the defaults
in any changes you make, should you wish to keep them:
# defaults + irc + mailto
uri_schemes => [ 'undef', 'http', 'https', 'irc', 'mailto' ]
* allow_declaration => [0|1]
Set this value to true if you'd like to allow/preserve DOCTYPE
declarations in your content. Useful when cleaning up your own
static files or templates. This feature is off by default.
my $html = q[foo];
my $hr = HTML::Restrict->new( allow_declaration => 1 );
$html = $hr->process( $html );
# $html is now: "foo"
* allow_comments => [0|1]
Set this value to true if you'd like to allow/preserve HTML comments
in your content. Useful when cleaning up your own static files or
templates. This feature is off by default.
my $html = q[foo];
my $hr = HTML::Restrict->new( allow_comments => 1 );
$html = $hr->process( $html );
# $html is now: "foo"
* replace_img => [0|1|CodeRef]
Set the value to true if you'd like to have img tags replaced with
"[IMAGE: ...]" containing the alt attribute text. If you set it to a
code reference, you can provide your own replacement (which may even
contain HTML).
sub replacer {
my ($tagname, $attr, $text) = @_; # from HTML::Parser
return qq{IMAGE: $attr->{alt}};
}
my $hr = HTML::Restrict->new( replace_img => \&replacer );
This attribute will only take effect if the img tag is not included
in the allowed HTML.
* strip_enclosed_content => [0|1]
The default behaviour up to 1.0.4 was to preserve the content
between script and style tags, even when the tags themselves were
being deleted. So, you'd be left with a bunch of JavaScript or CSS,
just with the enclosing tags missing. This is almost never what you
want, so starting at 1.0.5 the default will be to remove any script
or style info which is enclosed in these tags, unless they have
specifically been whitelisted in the rules. This will be a sane
default when cleaning up content submitted via a web form. However,
if you're using HTML::Restrict to purge your own HTML you can be
more restrictive.
# strip the head section, in addition to JS and CSS
my $html = '......foo';
my $hr = HTML::Restrict->new(
strip_enclosed_content => [ 'script', 'style', 'head' ]
);
$html = $hr->process( $html );
# $html is now '...foo';
The caveat here is that HTML::Restrict will not try to fix broken
HTML. In the above example, if you have any opening script, style or
head tags which don't also include matching closing tags, all
following content will be stripped away, regardless of any parent
tags.
Keep in mind that changes to strip_enclosed_content are not
additive, so if you are adding additional tags you'll need to
include the entire list of tags whose enclosed content you'd like to
remove. This feature strips script and style tags by default.
SUBROUTINES/METHODS
process( $html )
This is the method which does the real work. It parses your data,
removes any tags and attributes which are not specifically allowed and
returns the resulting text. Requires and returns a SCALAR.
CAVEATS
Please note that all tag and attribute names passed via the rules param
must be supplied in lower case.
# correct
my $hr = HTML::Restrict->new( rules => { body => ['onload'] } );
# throws a fatal error
my $hr = HTML::Restrict->new( rules => { Body => ['onLoad'] } );
MOTIVATION
There are already several modules on the CPAN which accomplish much of
the same thing, but after doing a lot of poking around, I was unable to
find a solution with a simple setup which I was happy with.
The most common use case might be stripping HTML from user submitted
data completely or allowing just a few tags and attributes to be
displayed. With the exception of URI scheme checking, this module
doesn't do any validation on the actual content of the tags or
attributes. If this is a requirement, you can either mess with the
parser object, post-process the text yourself or have a look at one of
the more feature-rich modules in the SEE ALSO section below.
My aim here is to keep things easy and, hopefully, cover a lot of the
less complex use cases with just a few lines of code and some brief
documentation. The idea is to be up and running quickly.
SEE ALSO
HTML::TagFilter, HTML::Defang, HTML::Declaw, HTML::StripScripts,
HTML::Detoxifier, HTML::Sanitizer, HTML::Scrubber
ACKNOWLEDGEMENTS
Thanks to Raybec Communications for funding my
work on this module and for releasing it to the world.
Thanks also to the following for patches, bug reports and assistance:
Mark Jubenville (ioncache)
Duncan Forsyth
Rick Moore
Arthur Axel 'fREW' Schmidt
perlpong
David Golden
Graham TerMarsch
Dagfinn Ilmari Mannsåker
Graham Knop
Carwyn Ellis
AUTHOR
Olaf Alders
COPYRIGHT AND LICENSE
This software is copyright (c) 2013 by Olaf Alders.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.